The proposed research plan is rooted in the notion that glutamate is a/the major neurotransmitter t the firs synapse established by peripheral nerve fibers in the central nervous system. Since peripheral nerve fibers with different functional characteristics release the same transmitter, postsynaptic mechanisms may be involved. These may include preferential termination of different types of afferent fibers onto different types of glutamate receptors. The first part of the proposed research will test this possibility. Peripheral nerve injury may result in hypergeusia, i.e. enhanced response to "painful" stimuli, that may be blocked by glutamate antagonists. The neuronal hyperexcitability that may underlie hyperalgesia may be explained by changes in the density or distribution of glutamate receptors in dorsal horn neurons. This is what the second part of the proposed research plans to determine. The research planned here has not been possible until now at the microscopic level for lack of adequate methods. A modification of electron microscopic postembedding immunogold makes now possible to compare with accuracy qualtitive and quantitive aspects of glutamate receptors in injured and control spinal cord material.